The present invention relates to door hardware for controlling disengagement of a door lock mechanism and more particularly to panic exit devices that permit easy opening of a door by movement of a push bar.
Building codes for publicly accessible structures typically require provision of marked emergency exits secured by a push bar activated emergency latch mechanism. This allows occupants of a structure to exit quickly and easily in an emergency. However, for many types of facilities it is not desirable to allow ready escape from the facility in non-emergency situations. One solution is to provide an alarm that activates whenever the door of an emergency exit is opened. As an improvement, the door itself can remain closed for a set period of time, typically five to fifteen seconds, as the alarm is sounded. This brief delay allows time for security personnel to detain an individual attempting to exit in a non-emergency situation, while still allowing easy exit in an emergency. Such exit delaying mechanisms are particularly useful for retail stores, schools, hospital, or nursing care facilities that need to control public access while still allowing escape in emergency situations.
One known mechanism for providing for a delay is described in U.S. Pat. No. 5,011,199, with inventors Lowe et al, and assigned to Von Duprin, Inc., the disclosure of which is hereby incorporated by reference. U.S. Pat. No. 5,011,199 describes a commercially available device that has a time delayed mechanism for obstructing movement of a latch bolt from a latched position to an unlatched position. Manual actuation of a push pad pivots an arm connected to a linkage. Movement of the linkage incidentally activates a time delay circuit component, which in turn controls interruption of electrical power to a solenoid. When powered, the electromagnetic attraction of the solenoid prevents movement of a bar/rod combination away from a position that effectively blocks full pivotable movement of the arm, preventing unlatching the door. After the preset time delay elapses (during which time visual or auditory alarms triggered by the attempt to open the emergency door are active) the electrical power to the solenoid is interrupted, allowing movement of the bar/rod combination away from their arm blocking position, and retraction of the latch bolt.
Another mechanism for ensuring a time delayed emergency exit is described in U.S. Pat. No. 5,085,475 to Austin et al., assigned to Von Duprin, Inc, the disclosure of which is hereby incorporated by reference. Like the device described in U.S. Pat. No. 5,011,199, the door exit delay mechanism described in Austin includes an electromagnetic solenoid and a movable limb having a lobe that obstructs pivoting movement of an arm connected to a latch. Inactivation of the solenoid, after a suitable time delay, allows displacement of the movable limb from the arm blocking lobe on the movable limb, permitting retraction of the latch and escape through the door exit.
Although reliable, exit delay mechanisms such as described in U.S. Pat. Nos. 5,011,199 or 5,085,475 can be inappropriate for certain circumstances. Such devices will generally activate an alarm and engage the time delay circuitry when the door is opened, even when the alarm and time delay are not needed or desired. This situation commonly arises for schools and hospitals, which may wish to allow free exit during normal hours, while allowing only emergency exit after hours. It would therefore be desirable to provide an exit delay system that can be selectively deactivated to allow unhindered exit within certain defined time periods, while still allowing simple conversion back to a full exit delaying, alarm activating system. It would also be desirable to provide a keyed lock system attachable to the door to allow engagment or disengagment of the exit delaying system. Such a key controlled exit delaying system advantageously allows simple control of each emergency exit, and selective disengagment of exit delay systems in non-critical areas of buildings. A mechanism for dogging controlled exit devices such as described in U.S. Pat. No. 5,085,475 to Austin et al., assigned to Von Duprin, Inc., or in U.S. Pat. No. 5,011,199, to Lowe et al, and also assigned to Von Duprin, Inc., by holding back operation of the latch bolt of the exit devices, would also be desirable.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.